Fan controllers which control the speed of a fan to maintain a relatively constant air temperature are well known and are described in U.S. Pat. Nos. 5,364,026; 4,722,669; and 4,659,290. These representative types of fan controllers employ an ambient air temperature sensor which provides a feedback signal to the fan controller which, in turn, adjusts the speed of the fan motor to maintain the air temperature within a specified range.
Such a fan controller is useful in cabinets which contain electronic equipment since the requirements for cooling vary with ambient air conditions, the particular types of electronic equipment housed within the cabinet, the utilization of the electronic equipment, and other factors which affect the cooling needs within the cabinet. Further, although it is generally adequate to operate the fan at a relatively high constant speed in order to consistently provide cooling for worst case conditions, the constant high speed consumes more energy, reduces the life of the fan, and generates a relatively high noise level.
Sensors for monitoring a fault in fan operation are also known. Such sensors, when detecting a fault, may operate to shut down the electronic equipment within the cabinet in anticipation that the equipment will eventually overheat. One such sensor is described in U.S. Pat. No. 5,448,143 and includes a current sensor that provides a signal indicative of the current through the fan. A pair of comparators detects whether the signal is within a proper range and, if the signal falls out of the range, it is presumed a fan fault has occurred. In response, a system shutdown or warnings occur.
Applicants have identified additional functions for a fan controller which have heretofore not been performed by a fan controller. This present disclosure describes circuitry which performs these functions.